This invention relates generally to telecommunication systems and more particularly, it relates to an alarm filter circuit used in telecommunication systems for interconnecting between incoming telephone lines and an alarm unit located at a subscriber""s premises so as to block DSL signals to and from the alarm unit for preventing interference.
It is generally well-known these days that many telephone subscribers or customers also have a personal computer located on their premises. At times, the computer user receives DSL (an acronym for Digital Subscriber Line) signals from the Internet over the same telephone lines via an Internet Service Provider (ISP). In addition, a number of telephone subscribers have an alarm system, such as burglar and/or fire, installed on their premises which is also connected to the same incoming telephone lines via internal house wiring. As a result, during an abnormal or alarm condition when the alarm modem is sending alarm signals to a monitoring station, the DSL signals will cause interference problems with the input circuitry of the alarm modem and will prevent the alarm signals from ever reaching the monitoring station. This problem is due to the input circuitry of the alarm modem not having sufficient low pass filtering above the frequency of 4 KHz since the upstream DSL signals will be at a relatively high level (several volts) beginning at the frequency of 25 KHz or above. Thus, the DSL signals will saturate the input circuitry of the alarm modem. Further, the interference problem will also produce distortion elements which will effectively reduce or limit the DSL data rates.
Accordingly, it would be desirable to provide an alarm filter circuit so as to prevent DSL signals from interfering with an alarm unit located at the subscriber""s premises and vice versa. It would be expedient that the alarm filter circuit be capable of a self-installed approach so as to allow the subscriber or customer to perform his own connection, thereby avoiding the time and cost for a trained technician to be sent to a subscriber""s premises to perform the installation. The alarm filter circuit of the present invention is of a modular type adapter designed so as to facilitate quick and easy connections between the incoming telephone lines and the alarm unit. The alarm filter circuit serves to block the DSL signals in the frequency band of 25 KHz to 1.1 MHZ from reaching the alarm unit.
Accordingly, it is a general object of the present invention to provide an alarm filter circuit which effectively and efficiently prevents DSL signals from interfering with an alarm unit located at a subscriber""s premises.
It is an object of the present invention to provide an alarm filter circuit used in telecommunication systems for interconnecting between incoming telephone lines and an alarm unit located at a subscriber""s premises.
It is another object of the present invention to provide an alarm filter circuit used in telecommunication systems for interconnecting between incoming telephone lines and an alarm unit located at a subscriber""s premises so as to block DSL signals from interfering with the alarm unit and vice versa.
It is still another object of the present invention to provide an alarm filter circuit which is of a modular type adapter designed so as to facilitate quick and easy connections between incoming telephone lines and an alarm unit.
It is still yet another object of the present invention to provide an alarm filter circuit which includes a low-pass filter section interconnected between incoming telephone lines and an alarm unit for preventing overloading of the alarm unit and a high-pass filter section for bypassing DSL data signals from the incoming telephone lines to the house wiring and around the low-pass filter section.
It is yet still another object of the present invention to provide an alarm filter circuit which includes a second-order or fourth-order elliptical low pass filter section and a first-order or third-order high-pass filter section.
In accordance with one preferred embodiment of the present invention, there is provided an alarm filter circuit used in telecommunication systems for interconnecting between incoming telephone lines and an alarm unit located at a subscriber""s premises so as to block DSL data signals to and from the alarm unit for preventing interference. The alarm filter circuit includes a second-order low-pass filter section formed of a first inductor, a second inductor, and a first capacitor; a first-order high-pass filter section formed of a second capacitor and a third capacitor; and a first-order low-pass filter section formed of a third inductor and a fourth inductor.
In a second embodiment of the present invention, the alarm filter circuit includes a fourth-order elliptical low-pass filter section formed of first through fourth inductors and first through fourth capacitors; a first-order high-pass filter section formed of a fifth capacitor and a sixth capacitor; and a first-order low-pass filter section formed of a fifth inductor and a sixth inductor. In a third embodiment of the present invention, the alarm filter circuit includes a fourth-order elliptical low-pass filter section formed of first through fourth inductors and first through fourth capacitors; a third-order high-pass filter section formed of a fifth through eighth capacitors and a fifth inductor; and a first-order low-pass filter section formed of a sixth inductor and a seventh inductor.
The foregoing applies specifically to the disclosure of the parent application Ser. No. 09/848,654. A fourth embodiment of an alarm filter circuit of the present invention added by way of this continuation-in-part application is quite similar to FIG. 2, except that the filter circuit thereof has been modified so as to include a capacitor C4 connected across the inductor L3 and L4. As a result, this fourth embodiment represents an improvement over the embodiment of FIG. 2 since it provides additional attenuation of the DSL signals so as to eliminate interference problems. In addition, there is provided optionally a sidactor or metal-oxide varistor D1, or other surge device such as a gas tube, connected across the incoming telephone lines. Further, slow-blow fuses F1, F2 may be optionally connected in series with the respective incoming telephone lines. The varistor D1 and the fuses F1, F2 function as surge protection means for preventing damage to the alarm filter circuit due to a power cross-over on the telephone lines.
In addition, a fifth embodiment of an alarm filter circuit of the present invention also added by way of this continuation-in-part application includes all of the components of the second embodiment of FIG. 3 and has further added a capacitor C7 connected across the inductors L3 and L4. Also, a sidactor or metal-oxide varistor D1 and slow-blow fuses F1, F2, which are identical to the ones added in the fourth embodiment, have also been included and function in the same manner.
In a sixth embodiment, there is provided an alarm filter circuit which includes all of the components of the third embodiment of FIG. 4 and has further added a capacitor C7 connected along the inductors L3 and L4. Also, a metal-oxide varistor D1 and slow-blow fuses F1, F2, which are identical to the ones added in the fourth and fifth embodiments, have also been included and function in the same manner.